Wind power is desirable because it is renewable and typically cleaner than fossil fuel power sources. Wind turbines capture and convert the energy of moving air to electric power. However, they do so unpredictably and often during low power demand periods when the value of electric power is substantially lower than during peak demand periods. Without a way to achieve certainty of delivery during peak demand periods (also known as “firm” power), and without a way to store low-value off-peak power for release during high-value peak periods, the growth of wind power and other intermittent renewable power sources may be constrained, keeping it from reaching its full potential as part of the world's overall power generation portfolio.
Another disadvantage of intermittent power sources such as wind is that they can cause system “balance” problems if allowed onto the transmission grid, which is a major hurdle for new (particularly renewable) power generation sources to clear. Operating wind turbines (or other intermittent renewable power assets) adjacent to and in conjunction with a natural gas—(NG) fired turbine can yield 100% certainty of power, because the NG turbine can “back up” the wind. However, that approach will yield a reduced environmental rating, based on the hours of operation for the NG turbine and may be economically unfeasible because the two power output systems need to be fully redundant, and thus capacity utilization and economic return-on-assets is diminished. Most importantly, neither a standard wind farm nor a back-up NG turbine(s) can “store” the wind power that may be widely available during the off-peak periods.
A disadvantage of other types of utility-scale power sources is that they produce large and unnecessary amounts of power during off-peak periods or intermittently. Another major disadvantage of existing power systems, both firm and intermittent, is that transmission lines often become “clogged” or overloaded, and transmission systems can become unbalanced. One existing solution for overloaded transmission lines is transferring power by “wheeling,” which is the delivery of a specific quantity of power to each end-user, allowing any “power product” to enter the power transmission system and be used to “balance” any other product that was removed from the system. A disadvantage of using current storage systems for wheeling is that power production occurs during all hours (most of which are not peak demand hours), and does not substantially overlap with peak demand hours. Another disadvantage is that transmission of power, which occurs at all hours (most of which are not peak demand hours), also does not substantially overlap with peak demand hours.
The few utility-scale power storage systems that exist today (or have been proposed previously) also have major disadvantages such as inefficient heat and cold recovery mechanisms, particularly those that require multiple systems for hot and cold storage media. Another disadvantage is extra complexity in the form of many expanders and compressors often on the same shaft with “clutches” that allow some front-end elements to be disconnected from the back-end elements on the same shaft. Some existing power plants use a simple cycle gas turbine with a recuperator, where a front-end compressor is on the same shaft as the hot-gas expander that compresses the inlet air. However, in that configuration some 63% of the power output is devoted to compressing inlet air.
Therefore, there exists a need for a system that can provide certainty and a firm, consistent energy output from any power source, particularly intermittent power sources such as wind. There is also a need to provide a convenient storage system for power that can be used in connection with power generation sources that generate large amounts of power during off-peak periods, including both firm (i.e., baseload) and intermittent power sources. There is a further need for a power storage and release assembly having more efficient hot and cold recovery mechanisms and simpler, more efficient, compression and expansion systems.